A provisioning script is essentially just a list of idempotent commands to run on the machine. But given the way that docker works, idempotence is not required -- if you change a command, Docker rolls back to a known state and runs the command.

A provisioning script might be slightly "higher-level" than a Dockerfile or shell script, but I find the difference is minimal, that the number of lines of code required are similar. Many provisioning tools provide libraries of pre-built recipes you can utilize; Docker provides a repository of pre-built images.

A Dockerfile is not a replacement for your favorite build script: it's a reliable foundation for defining, unambiguously, in which context to run your script. The Dockerfile's defining feature is that it has no implicit dependency: it only needs a working Docker install. Unlike your favorite build script, which may require "python" (but which version exactly?), ssh (but which build exactly?), gcc ( but...), openssl ( but...) and so on.